Amplifying circuits



Feb. 16, 1932. H. c. MUELLER AMPLIFYING CIRCUITS Filed Dec. 31, 1928 Z Z 6 Z V z is nnnu INVENTOR. f M

- ATTORNEY-5 Patented Feb. 16, 1932 UNITED STATES PATENT OFFICE HERMAN C. MUELLER, OF MILWAUKEE, WISCONSIN AMPLIFYING CIRCUITS Application filed December 31, 1928. Serial No. 329,397.

r This invention relates to improvements in flex circuit, however, is generally considered amplifying circuits such as are used in the as being more difficult of proper assembly reception of radio broadcast. than an ordinary radio frequency amplifier It is the object of the invention to provide and consequently I have chosen this more 5; a new and improved form of coupling bedifficult application of the invention by way 0 tween the successive inductanees of such a of illustration. Conventional symbols are circuit whereby relatively sharp tuning may used throughout to show the several electrical be efiected with a relatively high energy devices which enter into my improved circuit. transfer. By sharp11ess,Iwill be understood The antenna at is coupled through a in to refer to the condition which obtains when small fixed condenser to a compound inducan inductance is resonant to a comparatively tance made up of a variometer 12 and a very narrow band of frequencies at any given solenoid, or other equivalent coil, 13. The time. Obviously this condition is desirable other end of coil 13 is connected to a binding in a radio signal receiver, since it enables post at G which is intended to be grounded the operator to receive a selected signal and and will hereinafter be referred to as to eliminate signals of closely adjacent freground. The compound inductance madeup quencies. High selectivity, however, has of variometer 12 and winding 13 is shunted heretofore been obtained only at the expense by a variable condenser 14 capable of tuning of volume and for this reason I have emphait as desired. cu sized the fact that this invention is intended The first amplifying tube or triode 15 of to give good volume while maintaining a de the receiver is adapted to handle both radio sirable high selectivity. frequency currents and also currents at au- In the drawings: dio-frequeneies. Grid 16 is connected to a Figure 1 is a complete circuit diagram of grid coil inductance 17 shunted by a tuning an operative radio receiver of the reflex type variable condenser 18. The grid return embodying this invention. passes through the secondary winding 19 of Figure 2 is a slight modification of the i11- transformer 20 to ground, such winding bevention as it appears in an antenna coupler ing lay-passed by a fixed condenser 21. A suitable for use in the circuit of Figure 1, filament 22 of each of the triodes15, 25, and

or in any other radio frequency circuit. 26 is grounded on the negative side and is Figure 3 is a further modified antenna connected between terminals A- and A+, couphng device embodying the invention. the lead to the A- terminal being controlled Figure 4 shows the application. of the inby the usual rheostat 27. A smaller variable vention to an untuned radio frequency transcondenser 28 is connected between the grid former. return lead from grid coil 17 to the plate 30 Figure 5 is a detail view showing the meof triode 15 and serves to control feed-back chanical structure involved in coupling two through said tube. inductances in accordance with this inven- The output of plate 30 passes through the tion. usual radio frequency transformer including Like parts are identified by the same referan untuned primary at 31 and a secondary ence characters throughout the several views. or grid coil at 32 tuned by variable condenser lVhile I have chosen to illustrate the ap- 33. In place of this transformer, the special plication of my invention to a reflex circuit, design shown in Figured and hereinafter to it will be understood that theinvention is be described, may be substituted if desired.

* equally applicable to other circuits. A re- The primary 31 of the radio frequency transformer is supplied with current through the primary 34: of audio-frequency tansformer having secondary 35 connected to the grid of triode 26.

The grid coil 32 is connected to the grid through a grid leak and by-pass condenser as diagrammatically illustrated. The filament return may be made either to the positive or negative filament leads according to the type of triode employed as a detector. The plate output of this triode is led back through the primary winding 36 of transformer 20 to a binding post adapted to receive current at proper voltage.

The plate output of triode 26 leads to jack 37 having another lead to a positive binding post for high potential current. Any sort of reproducer may be coupled to the receiver at the ack 37. I

It will be seen from the foregoing description that the circuit illustrated in Figure 1 is of standard construction with the eX- ception of the coupling between the tuned antenna circuit and the tuned grid coil 17,

,such coupling remaining to be described.

The antenna coils 12 and 13 and the grid coil 17 are in non-inductive relation and are cou pled solely by capacity.

The various views show a number of expedients for effecting the desired capacity coupling in accordance with this invention. The particular device employed in the Figure 1 illustration consists of the capacity which exists between adjacent strands of wire and metallic strips or conductors. The metallic conductor 50 is positioned upon or within a portion of coil 13 and is insulated therefrom by means of some suitable interposed insulating means. Metallic conductor 51 is similarly positioned upon and insulated from a portion of grid coil 17. As a result of this arrangement, it will be noted that the antenna circuit is coupled to the grid circuit through two capacities and an intervening conductor 52. Vhile the capacitances 50 and 51 are illustrated in the form of metallic strips, it is not necessary that they be so arranged with reference to the antenna and grid circuits, since the coupling obviously does not depend in any way upon a specific shape of the strips. It is particularly to be noted that a preferred embodiment of this invention includes a capacity which extends across several turns of coils in each of the two circuits to be coupled. Thus the capacitance 50 is in capacitative relation to several turns of coil 13 and the capacitance 51 is in l ke relation to several turns of grid coil 17. In the Figure 2 diagram, merely a fragment of a receiver circuit is illustrated. Antenna is coupled to ground through a tuned coil 15 controlled by variable condenser 14;. A switch at 16 allows the antenna to be connected, either directly to the coil or capacitatively thereto, through the small fixed condenser 47. The grid coil 17 and its tuning condenser 18 are arranged as described with reference to Figure 1. I have shown the connection of grid coil 18 to be effected by means of metallic conductors 50 and 51 and the intervening lead 52. If desired, a special connection may be made be tween the antenna and this series of conductors by means of the condenser 53. This adds slightly to the volume, but decreases selectivity.

It will be noted that as in the former case, coupling is eflected through two capacitances and an interposed conductor. It is true, also, that the strips of metal shown at 50 and 51 are in capacitative relation to a large proportion of the turns of the two coils to be coupled. Selectivity may be controlled by the width of the strip of metal so employed. It is preferred that the strip should be approximately the length' of the coil. A strip of this character if narrow, will give high selectivity, whereas if the strip is wider, the tuning will be broadened and the volume correspondingly increased. In any event, however, the results as to volume and selectivity appear to be superior than those which are.

obtainable in the ordinary inductive couling.

Figure 5 shows a convenient means of applying the capacitative strips of a coil. Solenoid coils are chosen for the illustration. The coils 15 and 17 are wound respectively on tubular forms 54 and 55. A strip of metal such as tin-foil, or any other conductive metal, is fixed at 50 and 51 in the interior of the respective forms 54; and 55, the capacity strips being connected by conductor 52 as heretofore explained. It will be noted that the two strips of foil extend the full length of the coils with which'they are associated and as a result, are in capacitative relation with every turn. Thus the two coils 15 and 17 are connected by a compound capacity involving, first, the capacity of the several turns of coil with conductive strip 50, and, secondly,'the capacity of strip 51 with the turns of coil 17. Such an arrangement will give excellent results in a radio receiver and the relative selectivity may be controlled as desired by increasing or decreasing the width of one or both of the strips and 51.

Figure 3 shows a construction embodying the same sort of capacity coupling which is employed in Figures 1 and 2. The Figure 3 construction differs from that shown in Figure 2 primarily in the use of a primary 56 for energizing coil 45. The primary winding is directly connected between the antenna and ground and eliminates the necessity for using any connection, direct or capacitative, between the antenna and the tuned coil 45.

Figure 4: shows an alternative coupling in the nature of untuned radio frequency transformers which may be employed, if desired, between triodes l5 and 25, or any other thermionic valves in an amplifying circuit. A primary 31 receives the output from plate of triode 15 and may be coupled to a source of plate current supply in the ordinary way. The grid coil 32 is similar to grid coil with the exception that it is untuned. The two coils 31 and 32 are in non-inductive relation and are coupled capacitatively by means of the two capacitances 150 and 151 and the intervening conductor 520.

It will be apparent from the foregoing description that the invention is applicable to tuned and to untuned circuits and may be developed in a plurailty of mechanical forms, any of which is adequate to carry out the purposes of the invention. I prefer, however, in coupling an aerial circuit to a radio amplifier, to employ two tuned circuits for connection by the capacitances herein described.

I claim:

1. An electrical circuit comprising the combination of a plurality of successive tuned circuits substantially in mutual non-inductive relation, and a coupling between said circuits consisting of a plurality of capacitances in series each capacitatively related to a tuned circuit.

2. An electrical circuit comprising the combination of a plurality of successive tuned circuits substantially in mutual non-inductive relation, and a coupling between said circuit-s consisting of a conductor capacitatively cou pled to a plurality of turns of each of said inductances.

3. In a radio receiver, the combination with an antenna circuit and a grid circuit each including an inductance having a number of turns, of a metallic strip in capacitative relation to a plurality of the turns of each of said inductances, and conductive means connecting said strips.

4. In a radio receiver, the combination with an antenna circuit and a grid circuit each in cluding an inductance having a number of turns, of a metallic strip in capacitative relation to a plurality of the turns of each of said inductances, and conductive means connecting said strips, the width of such strips being such as to produce a desired degree of selectivity in the coupling between said inductances.

5. In a radio receiver, the combination of a plurality of successive circuits each including an inductance shunted by a variable condenser, of means coupling said circuits and including capacitances each capacitatively related to an inductance and conductively connected.

6. In a radio receiver, the combination of a plurality of successive circuits each including an inductance shunted by a Variable condenser, of means coupling said circuits and of said coils.

HERMAN C. MUELLER. 

